Field of the Invention
The present disclosure relates to a variable antenna and an apparatus for detecting a radio signal.
Description of the Related Art
In a conventional radio monitoring and direction finding system, when array antenna having the same antenna element and radius is arranged in a single bay, a very high/ultra-high frequency (V/UHF) band cannot be covered due to a wave characteristic.
For example, when the antenna element is a dipole antenna, if the antenna element having a constant length exceeds a specific frequency, an antenna performance may be rapidly reduced. When the radius of array antenna is greater than a specific distance in a single bay, a signal may not be distinguished from a spurious signal, and the spurious signal is increased in a spatial spectrum so that the direction of the signal cannot be estimated. Further, if the distance between array antennas is not spaced apart by a specific distance or greater, interference is increased due to a mutual coupling between heterogeneous array antennas located in different bays so that the direction of received signal cannot be estimated.
Accordingly, the radio monitoring and direction finding system may spatially separate heterogeneous array antennas having a different element length and may arrange in a plurality of bays in order to cover a wide frequency range. However, an installation space over a certain size should be provided for the radio monitoring and direction finding system.